Method of making magnetic gores



Nov. 22, 1949 G. CAMILL! METHOD OF MAKING MAGNETIC CORES Original Filed Nov. '7, 1945 .m & r m 0c F t o no t mm t hm A 2 .5 u G H Patented Nov. 22, 1949 METHOD. OF G MAGNETIC CORES.

Guglielmo Gamilli; Pittsfield, Mass., assignon to General Electric Company, a. corporation:..ofi

New York Original application November '7, 1,945, Seria1jNo. 627,226.. Divided'and this application May 15;, 1947, Serial No; 748,271

1 Claim.

This invention relates to magnetic cores for induction apparatus and more. particularly to the method of making multi section cores. This is a division or'myapplication, SeriaPNo. 627,226, filed November 7, 1945, nowlEatent No. 2,446,999, issued August; 17, 1948, and assigned to the same ass gnee.

Ring type magnetic cores, having a plurality of sections between which there are air gaps are used, among other places, in bushing type current transformers in order-topmventcore saturation andgive linear currentreproduction over a wide range of primary currents. This is especially important in bus differential protective systems in which the operation depends upon the differential output current of two or more current transformers. For large diameter cores or coreshaving a small radial build the type of core shown in my Patent 2,382,857, which is assigned to the assignee of this application, has proved very satisfactory but because the air gaps between the sections or segments of the core are not exactly uniform this type of core construction is not well suited to small diameter cores or cores having a large radial build because in those cases the non-uniformity of the air gaps would become excessive. A well known way of making multisegment ring type cores with uniform air gaps is to build the segments up out of core punchings which lie in radial planes. However, this necessitates the use of different shaped and. size punchings for each different diameter core and each core having a different radial build and consequently a different die for making the core laminations is required in all such cases.

In order to eliminate the above disadvantages of the prior art I cut the core laminae for magnetic strip on an automatic indexing machine which merely varies the length of the cut pieces. One such machine forms the subject matter of Somerville Patent 2,369,617 which is assignedto the present assignee. The laminae are then flatwise bent to conform to the curvature of the ring shaped or toroidal core and are then strain relief annealed and set in this bent shape.

An object of the invention is a new and improved method of making a multi-segment magnetic core.

The invention will be better understood from the, following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Inthe drawing Fig. 1 shows an axial section through a transformer embodying my invention, Fig. 2 is a perspective view of a completed core made in accordancewith the teachings-of; my, invention, and Fig. 3 isa. partially. diassembled' view illustrating oneof. the intermediate steps.

in the method ofzmaking my core.

Referring now tothe drawing and=more pare. ticularly to Fig. 1; there isshown thereinacore I surrounded by a winding 2 which may. bethe secondary winding.- ofa. bushing type current transformer in whichthe primary winding is. a. conductor; which passesthrough the center of the toroidal assembly shown insectionin Fig. 1.

In Fig. 2 the core: isshown:as-includingby way; of example twelve similar segments 3, of laminations, which are substantially equally spaced apart around an insulating cylinder 4 which may be made of any suitable material, such as cloth which has been saturated with a hardened phenolic resin. The segments 3 are clamped to the cylinder 4 by means of bands 5 which are preferably made of non-magnetic material, such as brass or stainless steel. The laminations in each segment are held together by bolts 6. The uniform gaps between adjacent segments are filled with any suitable material, such as Portland cement or sand held together by a resin binder.

In making my improved core the various length pieces of magnetic strip which are required are cut in any suitable manner such as by means of an automatic index shearing machine, an example of which is described in the above-identifled Somerville patent. For example, in the case of the twelve segment core illustrated, twelve equal length pieces corresponding to, say, the outer lamination of each segment are cut and then the machine will cut twelve more pieces of slightly lesser length which correspond to the next innermost lamination of each segment and so on until all of the laminations are cut. They are then stacked into groups with each group having one piece of each length arranged in order of length and each group is bolted together by bolts passing through registering holes in the laminae, which holes are also made by the same machine which cuts the laminae. The assembled and bolted together groups of laminations which, of course, are still flat are then placed about a steel mandrel 7 and clamps similar to the bands 5 in Fig. 2 but preferably made of steel are passed around the assembly and drawn up tight, thus curving all of the laminae and making the various bolted together stacks of laminae into the shape of toroidal segments 3. This assembly is then material, with theresult that the segments 3 are set in their proper shape. The clamping bands are then removed and segments 3 lifted away from the mandrel l, as shown in Fig. 3, after which they are transferred to the cylinder 4 in Fig. 2 which is of thesame size as the mandrel I. The non-magnetic clamping bands 5 are then placed around the core and drawn up tight and the ends Welded together as indicated at 8, after which the gaps between the segments are filled with any suitable material, examples of Which have previously been given. 7 It is a simple matter to calculate the progressively different size of flat cut laminae so that when they are fiatwise bent they will form true segments of a ring or toroid in which the sides of adjacent'ones lie parallel and thus provide uniform air gaps.

While there has been shown and described a particular embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the invention and, therefore, it is aimed in the appended claim to cover all such changes and modifications as fall within the true spirit andscope of the invention.

What'I claimas new and desire to secure by Letters Patent of the United States is:

The method of making a magnetic core which includes, cutting magnetic strip material into predetermined different length pieces each having a hole punched therethrough, assembling said pieces into a plurality of'groups in which said 4 pieces in each group are flat stacked one on top of the other in order of size, clamping the pieces in each group together by means of a bolt passed through them, arranging said groups on the outer surface of a metal cylinder with the clamping bolts extending radially and with the shortest piece in each group in contact with the outer surface of the cylinder, surrounding said groups with a clamp which is drawn up tight so as to give the pieces in each group a curvature similar to that of said cylinder and so as to provide uniform aps between adjacent groups, strain relief annealing said groups, removing said clamp, fastening said groups in the same relation to a similar cylinder of non-magnetic material, and filling the gaps between said groups with non-magnetic solid material.

GUGLIELMO CAMILLI.

REFERENCES CITED The following references are of record in the, file of this patent:

UNITED STATES PATENTS Great Britain Oct. 17, 1940 

